This invention relates to elastomeric springs, particularly for use as auxiliary jounce bumpers for shock absorbers and MacPherson type automobile strut assemblies.
In motor vehicles having wheel suspensions utilizing MacPherson suspension struts, an important aspect of the ride characteristics of the vehicle is determined by the spring rate characteristics of the elastomeric auxiliary spring which engages when the telescoping rod of the hydraulic damper or hydraulic shock absorber nears the end of its travel and approaches the outer shell of the shock absorber. This point in the travel of the strut is called full jounce. At finite distance approaching full jounce, the elastomeric auxiliary spring must engage the end of the shock absorber to gradually yet firmly slow down and stop the travel of the strut rod prior to the end of its mechanical travel path. It is very desirable to have variable spring rates in the elastomeric auxiliary spring to gradually decelerate and stop the movement of the strut rod prior to full jounce. Auxiliary springs of various shapes and configurations are known which are made of rubber. In general the rubber springs have at most a two stage spring rate curve which limits the flexibility of the designer in optimizing ride characteristics of the vehicle. A polyurethane foam spring structure is known which exhibits a two stage spring rate. This foam polyurethane is based on a micro cellular foam produced from a polyester reacted with a naphthalene diisocyanate. The disadvantage of the foam products made with this type of polyester naphthalene diisocyanate is that the prepolymer has a very short pot life indicating limited stability/not more than three hours, whereupon its viscosity becomes uncontrollable and the finished characteristics of the microcellular foam product is too irregular to be useful. Further the polyesters and naphthalene diisocyanate are relatively expensive and have handling problems in manufacturing since the polyester is a solid material and the naphthalene diisocyanate is an aromatic material which is generally considered slightly hazardous to handle. An object of the invention is to provide a spring device having multiple spring rates which allow the spring rate to progressively go from soft to very hard. A further object is to provide a configuration which upon collapsing during the stroke of the device on which it is mounted there is little growth of external circumscribed volume. A further object is to provide a light weight device. Yet another object is to provide a spring made of material which has little permanent set.